This has got to be one of my all-time favourite conversations. CalTech cosmologist Sean Carroll and I sat down over Skype and spent an hour chewing through some of the deepest questions of physics.. and then some! Things like.. Why does time run forward? Is matter fundamentally made of particles or waves? (Hint: It's waves. Waving fields, like stretched rubber sheets.) How can we understand the bizarre symmetries of the nuclear forces? What's the right interpretation of quantum mechanics, and why does it seem to work at more levels of analysis than it has a right to? Why do we say that the Many Worlds hypothesis is actually simpler than alternatives? Is there a bottom layer to reality? Does "turtles all the way down" make sense? How should we think about systems arising from the complexity of physics, like chemistry, biology, psychology, philosophy, morality? Can you get an "ought" from an "is"? Why does matter bend space-time? And why do so many physicists seem to hate philosophy?